electrical safety by cooper bussman

7/30/2019 electrical safety by cooper bussman

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16 2005 Cooper Bussmann

Electrical Safety

Introduction

ntroduction

There is a great deal of activity in the electrical industry concerning electrical

afety. The focus is on the two greatest electrical hazards to workers: shock

nd arc-flash. In recent years significant knowledge has been gained through

esting and analysis concerning arc-flash hazards and how to contend withhis type of hazard. This hazard exists when a worker is working on or near

xposed, energized electric conductors or circuit parts that have not been

laced in an electrically safe work condition. If an arcing fault occurs, the

remendous energy released in a fraction of a second can result in serious

njury or death. However, there is a great challenge in getting the message to

he populace of the electrical industry so that safer system designs and safer

work procedures and behaviors result. Workers continue to sustain life altering

njuries or death. NFPA 70E Standard for Electrical Safety In The Workplace,

004 Edition, is the foremost consensus standard on electrical safety.

Why is there an NFPA 70E? In 1976 a new electrical standards development

ommittee was formed to assist the Occupational Safety and Health

Administration (OSHA) in preparing electrical safety standards. This committee

n Electrical Safety Requirements For Employee Workplaces, NFPA 70E, was

eeded for a number of reasons, including: (1) the NEC is an installation

tandard while OSHA also addresses employee safety in the workplace, (2)

ot all sections in the NEC relate to worker safety and these are therefore of

ttle value to OSHA's focus and needs, (3) many safety related work and

maintenance practices are not covered, or not adequately covered, in the

NEC and (4) a national consensus standard on electrical safety for workers

id not exist, but was needed an easy to understand document that

ddresses worker electrical safety. The first edition was published in 1979.

Only Work On Equipment That

s In An Electrically Safe Work Condition

The rule for the industry and the law is dont work it hot, Per OSHA

910.333(a)(1) and NFPA 70E2004 130.1, workers should not work on or

ear exposed live parts except for two demonstrable reasons:1. Deenergizing introduces additional or increased hazards (such as cutting

ventilation to a hazardous location) or

2. Infeasible due to equipment design or operational limitations (such as when

voltage testing is required for diagnostics).

inancial considerations are not an adequate reason to work on or near

nergized circuits. To violate these regulations and practices is a violation of

ederal law, which is punishable by fine and/or imprisonment.

Note: deenergized electrical parts are considered as energized until all steps of

he lockout/tagout procedure are successfully completed [OSHA 1910.333(b)]

nd the equipment has been successfully put in an electrically safe work

ondition (NFPA 70E). Voltage testing of each conductor, which is a necessary

tep while completing the lockout/tagout procedure (putting the equipment in an

lectrically safe work condition), is considered as working on energized partser OSHA 1910.333(b) and NFPA 70E 2004 120.1.

Therefore, adequate personal protective equipment (PPE) is always required

uring the tests to verify the absence of voltage after the circuits are

eenergized and properly locked out/tagged out. Adequate PPE may also be

equired during load interruption and during visual inspection that verifies that

ll disconnecting devices are open.

So no matter how well a worker follows safe work practices, there will always

e a risk associated with electrical equipment even when putting equipment

n an electrically safe work condition. And there are those occasions where it

s necessary to work on energized equipment such as when a problem can

ot be uncovered by trouble shooting the equipment in a deenergized state.

What Can Be Done To Lessen the Risk?

There are a multitude of things that can be implemented to increase electrical

safety, from design aspects and upgrading systems, to training, implementing

safe work practices and utilizing personal protective equipment. Not all of

these topics can be covered in this section. The focus of this section willmainly concern some overcurrent protection aspects related to electrical

safety. For some other related electrical safety topics, read the Cooper

Bussmann Safety BASICs Handbook, Edition 2, and visit the Safety

BASICs web page at www.cooperbussmann.com.

Shock Protection

There are three shock approach boundaries required to be observed in NFPA

70E - 2004 Table 130.2; these shock approach boundaries are dependent

upon the system voltage. The significance of these boundaries for workers

and their actions while within the boundaries can be found in NFPA 70E or the

Cooper Bussmann Safety BASICs Handbook, Edition 2. See Figure 2 for a

graphic depiction of the three shock approach boundaries with the flash

protection boundary (following the section on Flash Hazard Assessment). For

hazard analysis and worker protection, it is important to observe the shockapproach boundaries together with the flash protection boundary (which is

covered in paragraphs ahead).

Although most electrical workers and others are aware of the hazard due to

electrical shock, it still is a prevalent cause of injury and death. One of the

best ways to help minimize the electrical shock hazard is to utilize finger-safe

products and non-conductive covers or barriers. Finger-safe products and

covers reduce the chance that a shock or arcing fault can occur. If all the

electrical components are finger-safe or covered, a worker has a much lower

chance of coming in contact with a live conductor (shock hazard), or the risk

that a conductive part falling across bare, live conductive parts creating an

arcing fault is greatly reduced (arc-flash hazard). Shown below are the new

CUBEFuses that are IP-20 finger-safe, in addition, they are very current-

limiting protective devices. Also shown are Sami fuse covers for covering

fuses, Safety J fuse holders for LPJ fuses, CH fuse holders available for a

variety of Cooper Bussmann fuses and disconnect switches, with fuse and ter-

minal shrouds. All these devices can reduce the chance that a worker, tool or

other conductive item will come in contact with a live part.

Disconnects

Sami Covers

Safety J HoldersCUBEFuse

CH Series Holders

Terminal Shrouds


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2005 Cooper Bussmann

Electrical Safety

Arc-Flash Protection

Arc Fault Basics

An electrician, that is in an energized panelboard or just putting a system in an

electrically safe work condition is potentially in a very unsafe place. A falling

knockout, a dislodged skinned wire scrap inadvertently left previously in the

panelboard or a slip of a screwdriver can cause an arcing fault. The temperature ofthe arc can reach approximately 35,000F, or about four times as hot as the

surface of the sun. These temperatures easily can cause serious or fatal burns

and/or ignite flammable clothing.

Figure 1 is a model of an arc fault and the physical consequences that can occur.

The unique aspect of an arcing fault is that the fault current flows through the air

between conductors or a conductor(s) and a grounded part. The arc has an

associated arc voltage because there is arc impedance. The product of the fault

current and arc voltage concentrated at one point, results in tremendous energy

released in several forms. The high arc temperature vaporizes the conductors in an

explosive change in state from solid to vapor (copper vapor expands to 67,000

times the volume of solid copper). Because of the expansive vaporization of

conductive metal, a line-to-line or line-to-ground arcing fault can escalate into a

three phase arcing fault in less than a thousandth of a second. The speed of the

event is so rapid that the human system can not react quickly enough for a worker

to take corrective measures. If an arcing fault occurs while a worker is in close

proximity, the survivability of the worker is mostly dependent upon (1) system design

aspects, such as characteristics of the overcurrent protective devices and (2)

precautions the worker has taken prior to the event, such as wearing personal pro-

tective equipment appropriate for the hazard.

Figure 1. Electrical Arc Model

The effects of an arcing fault can be devastating on a person. The intense thermal

energy released in a fraction of a second can cause severe burns. Molten metal is

blown out and can burn skin or ignite flammable clothing. One of the major causes

of serious burns and deaths to workers is ignition of flammable clothing due to an

arcing fault. The tremendous pressure blast from the vaporization of conducting

materials and superheating of air can fracture ribs, collapse lungs and knock

workers off ladders or blow them across a room. The pressure blast can cause

shrapnel (equipment parts) to be hurled at high velocity (can be in excess of 700

miles per hour). And the time in which the arcing event runs its course can be onlya small fraction of a second. Testing has proven that the arcing fault current

magnitude and time duration are the most critical variables in determining the ener-

gy released. Serious accidents are occurring at an alarming rate on systems of

600V or less, in part because of the high fault currents that are possible. But also,

designers, management and workers mistakenly tend not to take the necessary

precautions that they take when designing or working on medium and high voltage

systems.

The Role of Overcurrent Protective

Devices In Electrical Safety

The selection and performance of overcurrent protective devices play a significant

role in electrical safety. Extensive tests and analysis by industry has shown that the

energy released during an arcing fault is related to two characteristics of the

overcurrent protective device protecting the affected circuit. These two

characteristics are 1) the time it takes the overcurrent protective device to ope

and 2) the amount of fault current the overcurrent protective device lets-throug

For instance, the faster the fault is cleared by the overcurrent protective devic

lower the energy released. If the overcurrent protective device can also limit thcurrent, thereby reducing the actual fault current that flows through the arc, th

lower the energy released. Overcurrent protective devices that are current-lim

and thus may greatly reduce the current let-through, can have a great affect o

reducing the energy released. The lower the energy released the better for bo

worker safety and equipment protection.

The photos and recording sensor readings from actual arcing fault tests (next

page) illustrate this point very well. An ad hoc electrical safety working group,

within the IEEE Petroleum and Chemical Industry Committee, conducted thes

tests to investigate arc fault hazards. These tests and others are detailed in

Staged Tests Increase Awareness of Arc-Fault Hazards in Electrical Equipme

IEEE Petroleum and Chemical Industry Conference Record, September, 1997

313-322. This paper can be found at www.cooperbussmann.com under

Services/Safety BASICs. One finding of this IEEE paper is that current-limiting

overcurrent protective devices reduce damage and arc-fault energy (providedfault current is within the current-limiting range). To better assess the benefit o

limiting the current of an arcing fault, it is important to note some key thresho

injury for humans. Results of these tests were recorded by sensors on manne

and can be compared to these parameters:

Just Curable Burn Threshold: 80C / 175F (0.1 sec)

Incurable Burn Threshold: 96C / 205F (0.1 sec)

Eardrum Rupture Threshold: 720 lbs/ft2

Lung Damage Threshold: 1728 - 2160 lbs/ft2

OSHA Required Ear Protection Threshold: 85 db (for sustained time p

(Note: an increase of 3 db is equivalent to doubling the sound level.)

Test 4, Test 3 and Test 1: General

All three of these tests were conducted on the same electrical circuit set-up wavailable bolted three phase, short-circuit current of 22,600 symmetrical RMS

amps at 480V. In each case, an arcing fault was initiated in a size 1 combinat

motor controller enclosure with the door open, as if an electrician were workin

the unit live or before it was placed in an electrically safe work condition.

Test 4 and Test 3 were identical except for the overcurrent protective device

protecting the circuit. In Test 4, a 640 amp circuit breaker with a short-time de

protecting the circuit; the circuit was cleared in 6 cycles. In Test 3, KRP-C-601

601 amp, current-limiting fuses (Class L) are protecting the circuit; they opene

fault current in less than12 cycle and limited the current. The arcing fault was

initiated on the line side of the motor branch circuit device in both Test 4 and T

3. This means the fault is on the feeder circuit but within the controller enclosu

In Test 1, the arcing fault is initiated on the load side of the branch circuit

overcurrent protective devices, which are LPS-RK 30SP, 30 amp, current-limifuses (Class RK1). These fuses limited this fault current to a much lower amo

and clear the circuit in approximately 14 cycle or less.

Following are the results recorded from the various sensors on the mannequi

closest to the arcing fault. T1 and T2 recorded the temperature on the bare ha

and neck respectively. The hand with T1 sensor was very close to the arcing

T3 recorded the temperature on the chest under the cotton shirt. P1 recorded

pressure on the chest. And the sound level was measured at the ear. Some re

pegged the meter. That is, the specific measurements were unable to be

recorded in some cases because the actual level exceeded the range of the

sensor/recorder setting. These values are shown as >, which indicates that th

actual value exceeded the value given but it is unknown how high of a level th

actual value attained.


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Electrical Safety


Photos and results Test 4:

Staged test protected by circuit breaker with short-time delay (not a current-limiting overcurrent protective device). Short-time delay intentionally delayed opening for six cycles

(0.1 second). Note: Unexpectedly, there was an additional fault in the wireway and the blast caused the cover to hit the mannequin in the head. Analysis result in incident energy of

5.8 cal/cm2 and flash protection boundary of 47 inches per IEEE 1584.


Staged test protected by KRP-C-601SP Low-Peak Current-Limiting Fuses (Class L). These fuses were in their current-limiting range and cleared in less than a 12 cycle

(0.0083 seconds). Analysis results in incident energy of 1.58 cal/cm2 and flash protection boundary of 21 inches per IEEE 1584.


Staged test protected by LPS-RK-30SP, Low-Peak Current-Limiting Fuses (Class RK1). These fuses were in current-limiting range and cleared in approximately14 cycle

(0.004 seconds). Analysis results in incident energy of less than 0.2 cal/cm2 and flash protection boundary of less than 6 inches.

1 2 3

4 5 6

1 2 3

4 5 6

1 2 3

4 5 6


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Electrical Safety


A couple of conclusions can be drawn from this testing.

(1) Arcing faults can release tremendous amounts of energy in many forms in a very

short period of time. Look at all the measured values compared to key thresholds

of injury for humans given in a previous paragraph. Test 4 was protected by a 640

A, non-current limiting device that opened in 6 cycles or 0.1 second.

(2) The overcurrent protective devices characteristic can have a significant impact on

the outcome. A 601 amp, current-limiting overcurrent protective device, protects

the circuit in Test 3. The current that flowed was reduced (limited) and the clearing

time was 12 cycle or less. This was a significant reduction compared to Test 4.

Compare the Test 3 measured values to the key thresholds of injury for humans

and the Test 4 results. The measured results of Test 1 are significantly less than

those in Test 4 and even those in Test 3. The reason is that Test 1 utilized a much

smaller (30 amp), current-limiting device. Test 3 and Test 1 both show that there

are benefits of using current-limiting overcurrent protective devices. Test 1 just

proves the point that the greater the current-limitation, the more the arcing fault

energy may be reduced. Both Test 3 and Test 1 utilized very current-limiting fuses,

but the lower amp rated fuses limit the current more than the larger amp rated

fuses. It is important to note that the fault current must be in the current-limiting

range of the overcurrent protective device in order to receive the benefit of the

lower current let-through. See the diagram that depicts the oscillographs of Test 4,Test 3 and Test 1.

Non-Current Limiting

Test 1

Test 4

Test 3 Reduced Fault Current

via Current-Limitation

Current-Limitation: Arc-Energy ReductionCurrent-Limitation: Arc-Energy Reductionurrent-Limitation: Arc-Energy Reduction

Flash Protection Boundary (FPB)Must wear appropriate PPE

FPB dependent on fault level and time duration.

Equipment

Shock Approach Boundaries (dependent on system voltage)

Prohibited: Qualified persons only; PPE as if direct contact with live

Restricted: Qualified persons only.

Limited: Qualified or unqualified persons only if accompanied

by qualified person.

(3) The cotton shirt reduced the thermal energy exposure on the chest (T3 measured

temperature under the cotton shirt). This illustrates the benefit of workers wearing

protective garments.

Flash Hazard Assessment

NFPA 70E has developed requirements to reduce the risk of injury to workers

due to shock and arc-flash hazards. There are three shock approach bound-

aries required to be observed in NFPA 70E - 2004. As discussed, arc fault

currents can release tremendous amounts of energy. NFPA 70E 2004

requires that before a worker approaches exposed electric conductors or circuit

parts that have not been placed in an electrically safe work condition; a flash

hazard analysis shall be performed. The flash hazard analysis should

determine the flash protection boundary (FPB) and level of personal protective

equipment (PPE) that the worker must wear. The flash protection boundary is

the distance from the energized parts at which a worker could sustain a just

curable burn (bare skin) as a result of an arcing fault. A worker entering the

flash protection boundary must be qualified and must be wearing appropriate

PPE. Figure 2 depicts the flash protection boundary and the three shock

approach boundaries that shall be observed per NFPA 70E - 2004. In an actual

situation, before a worker is permitted to approach equipment with exposed,

energized parts, these boundaries shall be determined. In addition, the worker

shall be wearing the required level of PPE, which can be determined by

calculating the incident energy. Until equipment is placed in an electrically safe

work condition (NFPA 70E 2004 120.1, it is considered energized. It is

important to note that conductors and equipment are considered energize

when checking for voltage while putting equipment in an electrically safe w

condition.

The incident energy is a measure of thermal energy at a specific distancean arc fault; the unit of measure is typically in calories per centimeter squ

(cal/cm2). The distance from the fault in determining the incident energy

depends on the workers body position to the live parts. After determining

incident energy in cal/cm2, the value can be used to select the appropriate

personal protective equipment. There are various types of PPE with distin

levels of thermal protection capabilities termed Arc Thermal Performance

Exposure Values (ATPV) rated in cal/cm2. Note: the most common distan

which incident energy has been determined in tests is 18 inches. If it is

necessary to determine incident energy at a different distance, NFPA 70E

2004 and IEEE 1584 have equations that can be used in many situations

greater than 18 inches).

Both the FPB and PPE level are dependent on the available fault current

the overcurrent protective device - its clearing time and if it is current-limi

Knowing the available bolted short-circuit current, the arcing fault current

the time duration for the equipment supply overcurrent protective device

open, it is possible to calculate the Flash Protection Boundary (FPB) and

Incident Energy Exposure level. NFPA 70E - 2004 and IEEE 1584 provid

formulas for this critical information. By reviewing the calculations, it is

important to note that current-limiting overcurrent protective devices (whe

their current-limiting range) can reduce the required FPB and PPE level a

compared to non-current-limiting overcurrent protective devices.

Figure 2


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Electrical Safety


Simple Method for Flash Hazard Analysis

Anytime work must be done on or near energized electrical equipment or

quipment that could become energized, a flash hazard analysis shall be

ompleted. This flash hazard analysis includes, but is not limited to,

etermining:

1. The Incident Energy Exposure to select the level of PPE needed to complete the

task

2. The Flash Protection Boundary to know the approach point to the equipment

where PPE will be required.

Various information about the system may be needed to complete this analysis

ut the two pieces that are absolutely necessary are:

1. The available 3 bolted fault current

2. The fuse or circuit breaker type and amp rating.

Consider the following one-line diagram and then follow the examples that

ake the steps needed to conduct a Flash Hazard Analysis (The following

nformation utilizes formulas based upon IEEE 1584 Guide for Arc-Flash

Hazard Analysis.Steps necessary to conduct a Flash Hazard Analysis when using Low-Peak

uses and the Table 1: Arc-Flash Incident Energy Calculator.

1. Determine the available bolted fault current on the line side terminals of the

equipment that will be worked upon.

2. Identify the amperage of the Low-Peak fuse upstream that is protecting the panel

where work is to be performed.

3. Consult the Low-Peak Fuse Incident Energy Calculator, Table 1, next page, to

determine the Incident Energy Exposure (I.E.) available.

4. Determine the Flash Protection Boundary that will require PPE based upon the

incident energy. This can also be simplified by using the column for Flash

Protection Boundary (FPB) in Table 1.

5. Identify the minimum requirements for PPE when work is to be performed inside

of the FPB by consulting the requirements found in NFPA 70E - 2004.

or more information refer to Cooper Bussmann Safety BASICs Edition 2

Handbook on www.cooperbussmann.com or contact Application Engineering.

Example 1: Flash Hazard Analysis using

Cooper Bussmann Current Limiting Fuses.

The following is a simple method when using certain Cooper Bussmann fuses;

this method is based on actual data from arcing fault tests with Cooper

Bussmann current-limiting fuses. Using this simple method, the first thing thatmust be done is to determine the incident energy exposure. Bussmann has

simplified this process when using LPS-RK-(amp)SP, LPJ-(amp)SP,

LP-CC-(amp) or KRP-C-(amp)SP Low-Peak fuses or JJS-(amp) Tron fuses.

In some cases the results are conservative; see Note 7.

In this example, the line side OCPD in Figure 3 is a LPS-RK-600SP, Low-Peak

current-limiting fuse. Simply take the available 3 bolted short-circuit current

at the panel, in this case 42,000 amps, and locate it on the vertical column in

the Arc-Flash incident Energy Calculator table #1 on the following page. Then

proceed directly to the right to the 401-600A fuse column and identify the

incident energy (I.E.) and flash protection boundary FPB).

With 42,000 amps of 3 bolted short-circuit current available, the table shows

that when relying on the LPS-RK-600SP Low-Peak fuse to interrupt an arcing

fault, the incident energy is 0.25 cal/cm2

. Notice the variables required are theavailable 3 bolted fault current and the ampacity of the Low-Peak current-

limiting fuse. See Notes 7 and 8.

The next step in this simplified flash hazard analysis is to determine the Flash

Protection Boundary (FPB). With an incident energy exposure of 0.25 cal/cm 2

and using the same table, the Flash Protection Boundary (FPB) is

approximately 6 inches, which is found next to the incident energy value

previously located. See Note 6. This FPB distance means that anytime work is

to be performed inside of this distance, including voltage testing to verify that

the panel is deenergized, the worker must be equipped with the appropriate

PPE.

The last step in the flash hazard analysis is to determine the appropriate PPE

for the task. To select the proper PPE, utilize the incident energy exposure

values and the requirements from NFPA 70E. NFPA 70E has requirements for

PPE that are based upon the incident energy exposures. When selecting PPE

for a given application, keep in mind that these requirements from NFPA 70E

are minimum requirements. Having additional PPE, above what is required,

can further assist in minimizing the effects of an arc-flash incident. See Note 3.

Another thing to keep in mind is that PPE available on the market today does

not protect a person from the pressures, shrapnel, and toxic gases that can

result from an arc-blast, which are referred to as "physical trauma" in NFPA

70E-2004. Existing PPE is only utilized to minimize the potential for burns from

the arc-flash. See Notes 1 & 2.

600V 3Main lugonly panel

42,000 Amps Bolted Short-Circuit

Current Available

LPS-RK 600SP600A, Class RK1 Fuses

Answer0.25 cal/cm2

Incident Energy @18''6'' FPB

Figure 3


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Electrical Safety

Arc-Flash Incident Energy Calculator

Flash Hazard Analysis Tools on www.cooperbussmann.com

Cooper Bussmann continues to study this topic and develop more complete data and application tools.

Visit www.cooperbussmann.comfor interactive arc-flash calculators and the most current data.

Table 1: 1 - 600A

Cooper Bussmann Low-Peak LPS-RK_SP fuses and molded case circuit breakers (MCCB)

Incident Energy (I.E.) values expressed in cal/cm2, Flash Protection Boundary (FPB) expressed in inches.

Bolted Fault 1-100A 101-200A 201-400A 401-600A

Current (kA) Fuse MCCB Fuse MCCB Fuse MCCB Fuse MCCBI.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. F

1 2.39 29 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >2 0.25 6 0.25 6 5.20 49 >100 >120 >100 >120 >100 >120 >100 >120 >100 >3 0.25 6 0.27 7 0.93 15 >100 >120 >100 >120 >100 >120 >100 >120 >100 >4 0.25 6 0.35 8 025 6 0.35 8 20.60 >120 >100 >120 >100 >120 >100 >5 0.25 6 0.43 9 0.25 6 0.43 9 1.54 21 >100 >120 >100 >120 >100 >6 0.25 6 0.50 10 0.25 6 0.50 10 0.75 13 >100 >120 >100 >120 >100 >8 0.25 6 0.65 12 0.25 6 0.65 12 0.69 12 0.65 12 36.85 >120 >100 >

10 0.25 6 0.81 14 0.25 6 0.81 14 0.63 12 0.81 14 12.82 90 >100 >12 0.25 6 0.96 15 0.25 6 0.96 15 0.57 11 0.96 15 6.71 58 1.7014 0.25 6 1.11 17 0.25 6 1.11 17 0.51 10 1.11 17 0.60 11 1.9616 0.25 6 1.26 19 0.25 6 1.26 19 0.45 9 1.26 19 0.59 11 2.2218 0.25 6 1.41 20 0.25 6 1.41 20 0.39 8 1.41 20 0.48 10 2.4820 0.25 6 1.56 22 0.25 6 1.56 22 0.33 7 1.56 22 0.38 8 2.7422 0.25 6 1.72 23 0.25 6 1.72 23 0.27 7 1.72 23 0.28 7 3.00

24 0.25 6 1.87 24 0.25 6 1.87 24 0.25 6 1.87 24 0.25 6 3.2626 0.25 6 2.02 26 0.25 6 2.02 26 0.25 6 2.02 26 0.25 6 3.5328 0.25 6 2.17 27 0.25 6 2.17 27 0.25 6 2.17 27 0.25 6 3.7930 0.25 6 2.32 28 0.25 6 2.32 28 0.25 6 2.32 28 0.25 6 4.0532 0.25 6 2.47 29 0.25 6 2.47 29 0.25 6 2.47 29 0.25 6 4.3134 0.25 6 2.63 31 0.25 6 2.63 31 0.25 6 2.63 31 0.25 6 4.5736 0.25 6 2.78 32 0.25 6 2.78 32 0.25 6 2.78 32 0.25 6 4.8338 0.25 6 2.93 33 0.25 6 2.93 33 0.25 6 2.93 33 0.25 6 5.0940 0.25 6 3.08 34 0.25 6 3.08 34 0.25 6 3.08 34 0.25 6 5.3642 0.25 6 3.23 35 0.25 6 3.23 35 0.25 6 3.23 35 0.25 6 5.6244 0.25 6 3.38 36 0.25 6 3.38 36 0.25 6 3.38 36 0.25 6 5.8846 0.25 6 3.54 37 0.25 6 3.54 37 0.25 6 3.54 37 0.25 6 6.1448 0.25 6 3.69 39 0.25 6 3.69 39 0.25 6 3.69 39 0.25 6 6.4050 0.25 6 3.84 40 0.25 6 3.84 40 0.25 6 3.84 40 0.25 6 6.6652 0.25 6 3.99 41 0.25 6 3.99 41 0.25 6 3.99 41 0.25 6 6.9254 0.25 6 4.14 42 0.25 6 4.14 42 0.25 6 4.14 42 0.25 6 7.18

56 0.25 6 4.29 43 0.25 6 4.29 43 0.25 6 4.29 43 0.25 6 7.4558 0.25 6 4.45 44 0.25 6 4.45 44 0.25 6 4.45 44 0.25 6 7.7160 0.25 6 4.60 45 0.25 6 4.60 45 0.25 6 4.60 45 0.25 6 7.9762 0.25 6 4.75 46 0.25 6 4.75 46 0.25 6 4.75 46 0.25 6 8.2364 0.25 6 4.90 47 0.25 6 4.90 47 0.25 6 4.90 47 0.25 6 8.4966 0.25 6 5.05 48 0.25 6 5.05 48 0.25 6 5.05 48 0.25 6 8.7568 0.25 6 5.20 49 0.25 6 5.20 49 0.25 6 5.20 49 0.25 6 9.0170 0.25 6 5.36 50 0.25 6 5.36 50 0.25 6 5.36 50 0.25 6 9.2872 0.25 6 5.51 51 0.25 6 5.51 51 0.25 6 5.51 51 0.25 6 9.5474 0.25 6 5.66 52 0.25 6 5.66 52 0.25 6 5.66 52 0.25 6 9.8076 0.25 6 5.81 53 0.25 6 5.81 53 0.25 6 5.81 53 0.25 6 10.0678 0.25 6 5.96 53 0.25 6 5.96 53 0.25 6 5.96 53 0.25 6 10.3280 0.25 6 6.11 54 0.25 6 6.11 54 0.25 6 6.11 54 0.25 6 10.5882 0.25 6 6.27 55 0.25 6 6.27 55 0.25 6 6.27 55 0.25 6 10.8484 0.25 6 6.42 56 0.25 6 6.42 66 0.25 6 6.42 66 0.25 6 11.1086 0.25 6 6.57 57 0.25 6 6.57 57 0.25 6 6.57 57 0.25 6 11.3788 0.25 6 6.72 58 0.25 6 6.72 58 0.25 6 6.72 58 0.25 6 11.63

90 0.25 6 6.87 59 0.25 6 6.87 59 0.25 6 6.87 59 0.25 6 11.8992 0.25 6 7.02 60 0.25 6 7.02 60 0.25 6 7.02 60 0.25 6 12.1594 0.25 6 7.18 61 0.25 6 7.18 61 0.25 6 7.18 61 0.25 6 12.4196 0.25 6 7.33 61 0.25 6 7.33 61 0.25 6 7.33 61 0.25 6 12.6798 0.25 6 7.48 62 0.25 6 7.48 62 0.25 6 7.48 62 0.25 6 12.93

100 0.25 6 7.63 63 0.25 6 7.63 63 0.25 6 7.63 63 0.25 6 13.20102 0.25 6 7.78 64 0.25 6 7.78 64 0.25 6 7.78 64 0.25 6 13.46104 0.25 6 7.93 65 0.25 6 7.93 65 0.25 6 7.93 65 0.25 6 13.72106 0.25 6 8.09 66 0.25 6 8.09 66 0.25 6 8.09 66 0.25 6 13.98

Read notes on the page following these tables. Fuse results based on actual test data. Circuit breaker results are based on IEEE 1584 calculations.

If circuit breakers are not properly maintained, values can be considerably greater.


7/11


Electrical Safety

Arc-Flash Incident Energy Calculator

Flash Hazard Analysis Tools on www.cooperbussmann.com

Cooper Bussmann continues to study this topic and develop more complete data and application tools.

Visit www.cooperbussmann.comfor interactive arc-flash calculators and the most current data.

Table 1a: 601 - 2000A

Cooper Bussmann Low-Peak KRP-C_SP fuses and circuit breakers; low voltage power circuit breakers (w/std) (LVPCB)

ncident Energy (I.E.) values expressed in cal/cm2, Flash Protection Boundary (FPB) expressed in inches.

olted Fault 601-800A 801-1200A 1201-1600A 1601-2000A

Current (kA) Fuse LVPCB Fuse LVPCB Fuse LVPCB Fuse LVPCBI.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. FPB I.E. FPB

1 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >1202 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >1203 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >1204 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >1205 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >1206 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >1208 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120

10 75.44 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >12012 49.66 >120 >100 >120 73.59 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >12014 23.87 >120 >1.00 >120 39.87 >120 >100 >120 >100 >120 >100 >120 >100 >120 >100 >12016 1.94 25 31.22 >120 11.14 82 >100 >120 24.95 >120 >100 >120 >100 >120 >100 >12018 1.82 24 35.05 >120 10.76 80 >100 >120 24.57 >120 >100 >120 >100 >120 >100 >12020 1.70 23 38.87 >120 10.37 78 >100 >120 24.20 >120 >100 >120 >100 >120 >100 >12022 1.58 22 42.70 >120 9.98 76 >100 >120 23.83 >120 >100 >120 >100 >120 >100 >12024 1.46 21 46.53 >120 8.88 70 46.53 >120 23.45 >120 >100 >120 29.18 >120 >100 >12026 1.34 19 50.35 >120 7.52 63 50.35 >120 23.08 >120 >100 >120 28.92 >120 >100 >12028 1.22 18 54.18 >120 6.28 55 54.18 >120 22.71 >120 >100 >120 28.67 >120 >100 >12030 1.10 17 58.01 >120 5.16 48 58.01 >120 22.34 >120 >100 >120 28.41 >120 >100 >12032 0.98 16 61.83 >120 4.15 42 61.83 >120 21.69 >120 61.83 >120 28.15 >120 >100 >12034 0.86 14 65.66 >120 3.25 35 65.66 >120 18.59 116 65.66 >120 27.90 >120 >100 >12036 0.74 13 69.49 >120 2.47 29 69.49 >120 15.49 102 69.49 >120 27.64 >120 >100 >12038 0.62 11 73.31 >120 1.80 24 73.31 >120 12.39 88 73.31 >120 27.38 >120 >100 >12040 0.50 10 77.14 >120 1.25 18 77.14 >120 9.29 72 77.14 >120 27.13 >120 77.14 >12042 0.38 8 80.97 >120 0.81 14 80.97 >120 6.19 55 80.97 >120 26.87 >120 80.97 >12044 0.25 6 84.79 >120 0.49 10 84.79 >120 3.09 34 84.79 >120 26.61 >120 84.79 >12046 0.25 6 88.62 >120 0.39 8 88.62 >120 2.93 33 88.62 >120 26.36 >120 88.62 >12048 0.25 6 92.45 >120 0.39 8 92.45 >120 2.93 33 92.45 >120 26.10 >120 92.45 >12050 0.25 6 96.27 >120 0.39 8 96.27 >120 2.93 33 96.27 >120 25.84 >120 96.27 >12052 0.25 6 >100 >120 0.39 8 >100 >120 2.93 33 >100 >120 25.59 >120 >100 >12054 0.25 6 >100 >120 0.39 8 >100 >120 2.93 33 >100 >120 25.33 >120 >100 >120

56 0.25 6 >100 >120 0.39 8 >100 >120 2.93 33 >100 >120 25.07 >120 >100 >12058 0.25 6 >100 >120 0.39 8 >100 >120 2.93 33 >100 >120 24.81 >120 >100 >12060 0.25 6 >100 >120 0.39 8 >100 >120 2.93 33 >100 >120 24.56 >120 >100 >12062 0.25 6 >100 >120 0.39 8 >100 >120 2.93 33 >100 >120 24.30 >120 >100 >12064 0.25 6 >100 >120 0.39 8 >100 >120 2.93 33 >100 >120 24.04 >120 >100 >12066 0.25 6 >100 >120 0.39 8 >100 >120 2.92 33 >100 >120 23.75 >120 >100 >12068 0.25 6 >100 >120 0.39 8 >100 >120 2.80 32 >100 >120 22.71 >120 >100 >12070 0.25 6 >100 >120 0.39 8 >100 >120 2.67 31 >100 >120 21.68 >120 >100 >12072 0.25 6 >100 >120 0.39 8 >100 >120 2.54 30 >100 >120 20.64 >120 >100 >12074 0.25 6 >100 >120 0.39 8 >100 >120 2.42 29 >100 >120 19.61 120 >100 >12076 0.25 6 >100 >120 0.39 8 >100 >120 2.29 28 >100 >120 18.57 116 >100 >12078 0.25 6 >100 >120 0.39 8 >100 >120 2.17 27 >100 >120 17.54 111 >100 >12080 0.25 6 >100 >120 0.39 8 >100 >120 2.04 26 >100 >120 16.50 107 >100 >12082 0.25 6 >100 >120 0.39 8 >100 >120 1.91 25 >100 >120 15.47 102 >100 >12084 0.25 6 >100 >120 0.39 8 >100 >120 1.79 24 >100 >120 14.43 97 >100 >12086 0.25 6 >100 >120 0.39 8 >100 >120 1.66 22 >100 >120 13.39 93 >100 >12088 0.25 6 >100 >120 0.39 8 >100 >120 1.54 21 >100 >120 12.36 88 >100 >12090 0.25 6 >100 >120 0.39 8 >100 >120 1.41 20 >100 >120 11.32 83 >100 >12092 0.25 6 >100 >120 0.39 8 >100 >120 1.28 19 >100 >120 10.29 77 >100 >12094 0.25 6 >100 >120 0.39 8 >100 >120 1.16 18 >100 >120 9.25 72 >100 >12096 0.25 6 >100 >120 0.39 8 >100 >120 1.03 16 >100 >120 8.22 66 >100 >12098 0.25 6 >100 >120 0.39 8 >100 >120 0.90 15 >100 >120 7.18 61 >100 >120

100 0.25 6 >100 >120 0.39 8 >100 >120 0.78 13 >100 >120 6.15 55 >100 >120102 0.25 6 >100 >120 0.39 8 >100 >120 0.65 12 >100 >120 5.11 48 >100 >120104 0.25 6 >100 >120 0.39 8 >100 >120 0.53 10 >100 >120 4.08 41 >100 >120106 0.25 6 >100 >120 0.39 8 >100 >120 0.40 9 >100 >120 3.04 34 >100 >120

Read notes on the page following these tables. Fuse results based on actual test data. Circuit breaker results are based on IEEE 1584 calculations.

circuit breakers are not properly maintained, values can be considerably greater.


8/11


Electrical Safety


Steps necessary to conduct a Flash Hazard Analysis when using Low-Peak

fuses and Figures 6 and 7.

1. Determine the available bolted fault current on the line side terminals of the

equipment that will be worked upon.

2. Identify the amperage of the Low-Peak fuse upstream that is protecting the panel

where work is to be performed.

3. Consult the Low-Peak Fuse Incident Energy Chart, Figure 6, to determine the

Incident Energy Exposure available.

4. Determine the Flash Protection Boundary that will require PPE based upon the

incident energy. This can also be simplified by using the chart for Flash Protection

Boundary in Figure 7.

5. Identify the minimum requirements for PPE when work is to be performed inside

of the FPB by consulting the requirements found in NFPA 70E.

Notes for Flash Hazard Analysis Table

General Notes for fuses and circuit breakers:

Note 1: First and foremost, this information is not to be used as arecommendation to work on energized equipment. This information is to help

assist in determining the proper PPE to help safeguard a worker from the

burns that can be sustained from an arc-flash incident. This information does

not take into account the effects of pressure, shrapnel, molten metal spray, or

the toxic vapor resulting from an arc-fault.

Note 2: This data is based upon IEEE 1584 Guide for Arc-Flash Hazard

Analysis. These methods were created so that the PPE selected from the

calculated incident energy would be adequate for 98% of arc-flash incidents.

In up to 2% of incidents, incurable burns to the body and torso or death could

result. This was based upon PPE with standard arc ratings of 1.2, 8, 25, 40

and 100 cal/cm2. PPE with intermediate ATPV values can be utilized, but at

the next lower standard ATPV rating.

Note 3: PPE must be utilized any time that work is to be performed on or near

energized electrical equipment or equipment that could become energized.Voltage testing, while completing the lockout/tagout procedure (putting the

equipment in an electrically safe work condition), is considered as working on

energized parts per OSHA 1910.333(b).

Note 4: The data is based on 32mm (1-1/4) electrode spacing, 600V 3

ungrounded system, and 20 by 20 by 20 box. The incident energy is based

on a working distance of 18 inches, and the flash protection boundary is

based on 1.2 cal/cm2.

Note 5: The Low-Peak fuse information is based upon tests that were

conducted at various fault currents for each Cooper Bussmann KRP-C_SP

and LPS-RK_ SP fuse indicated in the charts. Actual results from incidents

could be different for a number of reasons, including different (1) system

voltage, (2) short circuit power factor, (3) distance from the arc, (4) arc gap, (5)

enclosure size, (6) fuse manufacturer, (7) fuse class, (8) orientation of theworker and (9) grounding scheme. 100A LPS-RK_SP fuses were the smallest

fuses tested. Data for the fuses smaller than that is based upon the 100A

data. Arc-flash values for actual 30 and 60A fuses would be considerably less

than 100A fuses, however, it does not matter since the values for the 100A

fuses are already so low.

Note 6: The fuse incident energy values were chosen not to go below

0.25cal/cm2 even though many actual values were below 0.25cal/cm2. This

was chosen to keep from encouraging work on energized equipment without

PPE because of a low FPB.

Note 7: This Arc-Flash Incident Energy Calculator Table can also be used for

LPJ_SP, JJS, and LP-CC fuses to determine the incident energy available and

flash protection boundary.

Note 8: These values from fuse tests and calculations for circuit breakers

into account the translation from available 3-phase bolted fault current to

arcing fault current.

Note 9: To determine the flash protection boundary and incident energy fo

applications with other fuses, use the equations in IEEE 1584 or NFPA 70

Note 10: The circuit breaker information comes from equations in IEEE 1

that are based upon how circuit breakers operate.

Note 11: Where the arcing current is less than the instantaneous trip setti

(IEEE 1584 calculation methods), the value for incident energy is given a

>100cal/cm2.

Note 12: The data for circuit breakers up to 400A is based on Molded Ca

Circuit Breakers (MCCB) with instantaneous trip, for 401-600A it is based

MCCBs with electronic trip units, and the data for circuit breakers from 60

to 2000A is based on Low Voltage Power Circuit Breakers (LVPCB) with

short time delay. Per IEEE 1584 the short time delay is assumed to be se

maximum.

Note 13: The data for circuit breakers is based upon devices being prope

maintained in accordance with manufacturers instructions and industrystandards. Devices that are not properly tested and maintained may have

longer clearing times resulting in higher incident energies.

Method For Other Type Fuses

Table 1 is applicable for Low-Peak and Tron fuses. To determine the flash

protection boundary and incident energy for applications with other fuses

Low-Peak fuses under different parameters, use the equations in IEEE 15

Guide for Arc-Flash Hazard Analysis, or NFPA 70E-2004. The following a

formulas in NFPA 70E - 2004 for calculating the flash protection boundary

incident energy. It is significant to note that the flash protection boundary

dependent upon the available bolted short-circuit current (incorporated in

MVAbf) (or the let-through current if the overcurrent protective device is

current-limiting) and the opening time of the overcurrent protective device

Note, the results from these calculations will differ from the results obtainfrom the simple table method just covered. These formulas were derived

a broad base of empirical test data and were state of the art when introdu

The simple table method has some artificially conservative assumptions a

stated in the notes.

Flash Protection Boundary Calculation

Dc = (2.65 MVAbf x t)1/2

Df = (1.96 MVAbf x t)1/2*

where

Dc = distance in feet for a just curable burn

Df = distance in feet for an incurable burn*

MVAbf = bolted three phase MVA at point of short-circuit

= 1.73

VOLTAGEL-L

AVAILABLE SHORT-CIRCUITCURRENT l0-6

t = time of exposure in seconds

*Not included in NFPA 70E.

NFPA 70E 2004 Annex D provides equations for calculating incident en

under some common circumstances. For instance, the incident energy

equation for an arcing fault contained in a cubic box (20 inches on each s

opened on one end), on 600V or less systems, with available bolted shor

circuit currents of between 16,000 to 50,000 amps is as follows:


9/11


Electrical Safety


Example 2: Flash Hazard Analysis For

Circuit Breakers Using The Table Method.

**WARNING** If a Circuit Breaker has not been exercised, tested. and

maintained per manufacturers instructions and industry standards (NFPA

70B and other standards), then a longer clearing time may occur, resulting

in a higher incident energy calculation. Consult www.cooperbussmann.com,

or www.NETA.org for more information or technical papers on testing and

maintenance and/or consequences to potential arc-flash hazard.

The following is a simplified method using table 1 as done in example 1.

nstead of using LPS-RK-600SP, 600A, current-limiting fuse, we will use a

00A Molded Case Circuit Breaker.With the same 3 available short-circuit current current as in example #1,

2,000 amps, locate this on the vertical column (Bolted Fault Current kA) of

able 1. Then proceed directly to the right over to the 401-600A MCCB

Column. Then record the I.E. (Incident Energy) which should be 5.62 cal/cm2.

Also, record the value for the FPB (Flash Protection Boundary) which is 51

nches.

The last step in the flash hazard analysis is to determine the appropriate PPE

or the task.

f the circuit breaker in question is a power circuit breaker with short time delay

eature (no instantaneous trip), the incident energy calculation will increase.

or example, with a short time delay feature set at 30 cycles the incident

nergy at this available fault current could be as high as 67.680.97 cal/cm2 at

8 inches from the arc fault source.The following staged arc-flash test resulted in an incident energy of 5.8 cal/cm 2

nd a flash protection boundary of 47 inches using IEEE 1584 calculation

method.

requirements as shown in Table 130.7(C)(8) of NFPA 70E-2004. The selection

of the required thermal rated PPE depends on the incident energy level at the

point of work.

As stated previously, the common distance used for most of the low voltage

incident energy measurement research and testing is at 18 inches from the

arcing fault source. So what energy does a body part experience that is closer

to the arc fault than 18 inches? The closer to the arcing fault the higher the

incident energy and blast hazard. This means that when the flash protection

analysis results in relatively high incident energies at 18 inches from the arc

fault source, the incident energy and blast energy at the point of the arc faultcan be considerably greater. Said in another way, even if the body has

sufficient PPE for an 18" working distance, severe injury can result for any part

of the body closer than 18" to the source of the arc.

Exposure Time

As the previous sections have illustrated, the interruption time of overcurrent

protective devices is a major factor in the severity of an arc-flash. Following is

a table for some general minimum overcurrent protective device interruption

times that can be used for the FBP and incident energy calculations if this

data is not available from the manufacturer. STD Setting refers to the short

time delay setting if a circuit breaker has this feature; typical STDs settings

could be 6, 12, 18, 24, or 30 cycles. If an arc-flash analysis is being done for a

circuit breaker with adjustable settings, then the maximum settings should be

used for the analysis. If the lowest settings are used for the analysis, yet amaintenance person has inadvertently increased the setting to the maximum,

then the analysis could yield results that are incorrect and lower than required

for proper personnel protection.Type of Device Minimum Time (Seconds)*

Current-limiting fuse 0.004

Circuit Breaker (5kV & 15kV) 0.1

Standard molded case circuit

breakers (600V & below)

without short-time-delay (STD) 0.0083-0.0167

with short-time-delay (STD) STD Setting

Insulated case circuit breakers

(600V & below)

without short-time-delay 0.033

with short-time-delay STD Setting

Low voltage power (air frame)circuit breakers (600V & below)

without-short-time-delay 0.05

with short-time-delay STD Setting

Current-limiting molded case

circuit breaker (600V & below) 0.004

* These are approximate times for short-circuit currents within the current-limiting range of a

fuse or within the instantaneous region of circuit breakers. Lower current values may cause

the overcurrent device to operate more slowly. Arc-flash energy may actually be highest at

lower levels of available short-circuit current. This requires that arc-flash energy calculations

be completed for the range of sustainable arcing currents. Where equivalent RMS let-through

data (this is reduced let-through current due to current-limitation) is available, it can be used in

the flash distance and incident energy formula. Where data is unavailable, the full available

short-circuit must be used.

ncident Energy Calculation (20" cubic box)

EMB = 1038.7 DB-1.4738tA[0.0093F

2 -.3453F+5.9675] cal/cm2

Where: EMB = Incident Energy (cal/cm2)

DB = Distance, (in.) [for Distances 18 inches

]tA = Arc Duration, (sec.)

F = Bolted Fault Short Circuit Current kA [16kA to 50kA]

FPB: 47 Inches I.E.: 5.8 cal/cm2

The test parameters were:

Available fault current = 22,600A at 480Vac.

OCPD clearing time of six cycles or 0.1 second.

The level of PPE for this would have to be greater than 5.8 cal/cm2 andresult in a Hazard Risk Category 2.

Personal Protective Equipment (PPE)

Employees must wear and be trained in the use of

appropriate protective equipment for the possible electrical

hazards with which they may face. Examples of equipment

could include a hard hat, face shield, flame resistant neckprotection, ear protectors, Nomex suit, insulated rubber

gloves with leather protectors, and insulated leather

footwear. All protective equipment must meet the


10/11


Electrical Safety


Expect the Worst Case

If planning to work on a piece of equipment, it is necessary to do the flash

hazard analysis for the worst-case situation that could occur if an incident

occurred. For instance, in the diagram below, if the combination controller door

were to be opened, the worst-case arc-flash hazard in the enclosure would beon the line-side of the branch-circuit circuit breaker. If an arcing fault occurred

in the enclosure, on the line side of the of the branch-circuit circuit breaker, the

400 amp feeder circuit breaker is the protective device intended to interrupt.

So the flash hazard analysis for this combination motor controller enclosure

must be determined using the characteristic of the 400 amp feeder circuit

breaker.

equipment. Current-limiting overcurrent protection may reduce the r isk. In

other words, if an incident does occur, current-limiting overcurrent protec

devices may reduce the probability of a severe arc-flash. In many cases,

current-limiting protective devices greatly reduces the arc-flash energy th

might occur for the range of arc fault currents that are likely. However, culimiting overcurrent protective devices do not mitigate the potential hazar

all situations. This is especially true as the overcurrent protective devices

into the larger amp sizes. But all things being equal, systems with protec

devices that have a high degree of current-limitation generally lower the r

But it is still necessary to follow all the requirements of NFPA 70E and ot

safe work practices.

General Recommendations For Electrical Safety

Relative to Overcurrent Protection

(1) Finger-safe products and terminal covers: utilize finger-safe overcurrent pro

devices such as the CUBEFuse or insulating covers over the overcurrent

protective devices, disconnect terminals and all terminations.

(2) Proper interrupting rating: be absolutely sure to use overcurrent protective d

that have adequate interrupting ratings at their point of application. An overcprotective device that attempts to interrupt a fault current beyond its interrup

rating can violently rupture. Consideration for interrupting rating should be fo

life of the system. All too often, transformers are replaced or systems are

upgraded and the available short-circuit currents increase. Modern fuses ha

interrupting ratings of 200,000 and 300,000 amps, which virtually eliminates

hazard contributor.

(3) Current-limiting overcurrent protection: use the most current-limiting overcur

protective devices possible. There are a variety of choices in the market for

overcurrent protective devices. Many are not marked as current-limiting and

therefore can not be considered current-limiting. And then for those that are

marked current-limiting, there are different degrees of current-limitation to

consider. For Cooper Bussmann, the brand to use for 600V and less, electr

distribution applications and general equipment circuit protection is Low-Pea

fuses. The Low-Peak family of fuses is the most current-limiting type fuse fa

for general protection and motor circuit protection.

(4) Upgrade existing fuse systems: if the electrical system is an existing fusible

system, consider replacing the existing fuses with the Low-Peak family of fu

the existing fuses in the clips are not the most current-limiting type fuses,

upgrading to the Low-Peak family of fuses can reduce the hazards associat

with arc-flash. Visit www.cooperbussmann.com to review a service for the L

Peak upgrade, referred to as the Productivity Protector.

(5) Install current-limiting overcurrent protection for actual loads: if the actual m

mum full load current on an existing main, feeder or branch circuit is signific

below its designed circuit ampacity, replace the existing fuses with lower am

rated Low-Peak fuses. Or, if the OCPD is a circuit breaker, put a fused disco

with Low-Peak fuses in series with the circuit breaker. For instance, an indu

found that many of their 800 amp feeders to their MCCs were lightly loaded

better arc-flash protection they installed 400 and 600 amp current-limiting fu

and switches in the feeders.

(6) Reliable overcurrent protection: use overcurrent protective devices that are

reliable and do not require maintenance to assure performance per the orig

specifications. Modern fuses are reliable and retain their ability to react quic

under fault conditions. When a fuse is replaced, a new factory calibrated fus

put into service the circuit has reliable protection with performance equal t

original specifications. If mechanical overcurrent protective devices are utiliz

sure to perform the manufacturers recommended periodic exercise, mainte

testing and possible replacement. When an arc fault or overcurrent occurs,

overcurrent protective device must be able to operate as intended. Thus, fo

mechanical overcurrent protective devices, this may require testing, mainte

and possible replacement before resetting the device after a fault interruptio

400ASTD = 12 cycles

480V 3O MCC

M M

Arcing faultcould occurhere

Instantaneous tripbreaker with cycleclearing time

Other Arc Fault Hazards

An arcing fault may create such enormous explosive forces that there is a

huge blast wave and shrapnel expelled toward the worker. Neither NFPA

70E 2004 nor IEEE 1584 account for the pressures and shrapnel that can

result due to an arcing fault. There is little or no information on protecting a

worker for these risks.On a somewhat positive note, because the arc pressure blows the worker

away, it tends to reduce the time that the person is exposed to the extreme

heat of the arc. The greater the fault current let-through, the greater the explo-

sive forces. It is important to know that product standards do not evaluate a

product for a workers exposure to arc-flash and blast hazards with the door(s)

open. Equipment listed to a Nationally Recognized Testing Laboratory product

standard is not evaluated for arc-flash or arc blast

protection (with the door(s) open) because the equipment is tested with the

doors closed. Once a worker opens the doors, the parameters under the

evaluation testing and listing do not apply.

Caution: (1) A worker using PPE with adequate cal/cm2 ratings for high

incident energy arc-flash hazards may still incur severe injury or death due to

the arc blast or shrapnel. For instance, review the results for Test 4 on page

118. Generally, the higher the incident energy, the higher the blast energy that

will result. (2) For systems 600V and less, NFPA 70E 2004 has an

alternate method to find the flash protection boundary (four foot qualified

default) and PPE selection (using two tables a. hazard risk category by

tasks table and b. PPE and tools for each hazard risk category table).

Although, these methods can be more convenient, there are very important

qualifiers and assumptions in the tables notes and legends. It is possible for a

specific situation to be beyond the assumptions of these tables and therefore,

in these situations, the tables are not to be used.

Summary About the Risks From Arc Faults

Arc faults can be an ominous risk for workers. And an uneducated eye can not

identify whether the risk is low, medium or high just by looking at the


11/11

26 2005 C B

Electrical Safety


(7) Within sight motor disconnects: install Hp rated disconnects (with permanently

installed lockout provision) within sight and within 50 feet of every motor or driven

machine. This measure fosters safer work practices and can be used for an

emergency disconnect if there is an incident.

Flash Protection Field Marking:New NECRequirement

110.16 Flash Protection: Switchboards, panelboards, industrial control

panels, meter socket enclosures and motor control centers in other than

dwelling occupancies, that are likely to require examination, adjustment,

servicing, or maintenance while energized, shall be field marked to warn

qualified persons of potential electric arc-flash hazards. The marking shall

be located so as to be clearly visible to qualified persons before

examination, adjustment, servicing, or maintenance of the equipment.

FPN No. 1: NFPA 70E-2004 Standard for Electrical Safety in the Workplace

provides assistance in determining severity of potential exposure, planning

safe work practices, and selecting personal protective equipment.

FPN No. 2: ANSI Z535.4-1998, Product Safety Signs and Labels, provides

guidelines for the design of safety signs and labels for application toproducts.

Reprinted from NEC 2005

This new requirement is intended to reduce the occurrence of serious injury or

eath due to arcing faults to workers who work on or near energized electrical

quipment. The warning label should remind a qualified worker who intends to

pen the equipment for analysis or work that a serious hazard exists and that

he worker should follow appropriate work practices and wear appropriate

ersonal protective equipment (PPE) for the specific hazard (a non-qualified

worker must not be opening or be near open energized equipment).

005 NEC 110.16 only requires that this label state the existence of an arc-

ash hazard.

Where To Get Help

Professional Services

Cooper Bussmann provides electrical safety services including:

1. Electrical system one-line diagram development

2. Short-circuit current analysis

3. Overcurrent protective device time-current curve characteristic analysis

4. Overcurrent protective device coordination analysis

5. Arc-flash hazard analysis

6. Arc-flash hazard label production

7. Electrical safety program development

8. Electrical safety training

9. Annual maintenance

Contact your local Cooper Bussmann sales engineer or call 636-207-3294.

Materials to Help Understand the Issues and

Solutions

Go to www.cooperbussmann.com under electrical safety. There is an

on-line arc-flash hazard calculator, several technical papers, Safety BASICs

Handbook Edition 2, and more.

Training Kits

There are two kits to assist in training personnel. Part # SBK Safety

BASICs Kit for trainers, which includes handbook, many electronic

presentations following the handbook, video, and more. Part # SBTH Safety

BASICs Kit for participants includes 10 copies of the handbook and

participants guides. These can be ordered from authorized Cooper

Bussmann distributors. Description on www.cooperbussmann.com under

Safety BASICs.

is suggested that the party responsible for the label include more information

n the specific parameters of the hazard. In this way the qualified worker and

is/her management can more readily assess the risk and better insure proper

work practices, PPE and tools. The example label following includes more ofhe vital information that fosters safer work practices. The specific additional

nformation that should be added to the label includes:

Available 3 Short-Circuit Current

Flash Protection Boundary

Incident energy at 18 inches expressed in cal/cm2

PPE required

Voltage shock hazard

Limited shock approach boundary

Restricted shock approach boundary

Prohibited shock approach boundary

electrical safety by cooper bussman

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